1. Field of the Invention
The present invention relates to a producing method of a pneumatic tire having a sidewall portion formed with a line or a character of color different from that of a main body rubber.
2. Description of the Related Art
Conventionally, to enhance the fashion, there is a known pneumatic tire having a sidewall portion formed with a line or a character of color different from that of a main body rubber. For example, in a sidewall portion 31 shown in FIG. 6, a black rubber layer 7 having the same color as that of a main body rubber and a white rubber layer 8 having a different color from that of the main body rubber are disposed. A thin cover rubber layer 9 having the same color as that of the main body rubber is disposed on an outer side of the white rubber layer 8. After vulcanization, if the cover rubber layer 9 is partially cut down by buffing to expose the white rubber layer 8, a white line or character can be formed on the sidewall portion 2 (see the following Japanese Patent Application Laid-open No. 9-1694).
A sidewall rubber constituting the sidewall portion is formed by an extrusion method or a ribbon winding method. According to the former method, a rubber extrudate having a predetermined cross section shape is integrally extruded, the rubber extrudate is wound along a circumferential direction of a tire once to constitute a sidewall rubber. However, since it is necessary to prepare a large number of sidewall rubber members corresponding to various tire sizes, there is a problem that the number of parts is increased, and since a step is generated in a joint portion, uniformity of tires is deteriorated.
According to the latter method, on the other hand, a rubber ribbon having small width and small thickness is wound along the circumferential direction of the tire a plurality of times to constitute the sidewall rubber. Therefore, the uniformity of tires is excellent, and the number of parts can be reduced. However, when a sidewall portion is formed with a line or a character of color different from that of a main body rubber, if the cover rubber layer is cut down by buffing, a profile of this portion becomes wavy along a cross section of the rubber ribbon in some cases, and there is a problem that an outward appearance of the tire is deteriorated. In the following International Publication No. 04/037524 Brochure, there is proposed a method in which a sidewall rubber is formed by ribbon winding method, a rubber sheet is wound once to form a cover rubber layer, and a portion of the cover rubber layer to be cut down is formed with a convex shape at the time of vulcanization. However, its profile becomes wavy along the cross section of a rubber ribbon having a color different from that of a main body rubber in some cases.